/**
 * Software License, Version 1.0
 * 
 * Copyright 2003 The Trustees of Indiana University.  All rights reserved.
 * 
 *
 *Redistribution and use in source and binary forms, with or without 
 *modification, are permitted provided that the following conditions are met:
 *
 *1) All redistributions of source code must retain the above copyright notice,
 * the list of authors in the original source code, this list of conditions and
 * the disclaimer listed in this license;
 *2) All redistributions in binary form must reproduce the above copyright 
 * notice, this list of conditions and the disclaimer listed in this license in
 * the documentation and/or other materials provided with the distribution;
 *3) Any documentation included with all redistributions must include the 
 * following acknowledgement:
 *
 *"This product includes software developed by the Community Grids Lab. For 
 * further information contact the Community Grids Lab at 
 * http://communitygrids.iu.edu/."
 *
 * Alternatively, this acknowledgement may appear in the software itself, and 
 * wherever such third-party acknowledgments normally appear.
 * 
 *4) The name Indiana University or Community Grids Lab or NaradaBrokering, 
 * shall not be used to endorse or promote products derived from this software 
 * without prior written permission from Indiana University.  For written 
 * permission, please contact the Advanced Research and Technology Institute 
 * ("ARTI") at 351 West 10th Street, Indianapolis, Indiana 46202.
 *5) Products derived from this software may not be called NaradaBrokering, 
 * nor may Indiana University or Community Grids Lab or NaradaBrokering appear
 * in their name, without prior written permission of ARTI.
 * 
 *
 * Indiana University provides no reassurances that the source code provided 
 * does not infringe the patent or any other intellectual property rights of 
 * any other entity.  Indiana University disclaims any liability to any 
 * recipient for claims brought by any other entity based on infringement of 
 * intellectual property rights or otherwise.  
 *
 *LICENSEE UNDERSTANDS THAT SOFTWARE IS PROVIDED "AS IS" FOR WHICH NO 
 *WARRANTIES AS TO CAPABILITIES OR ACCURACY ARE MADE. INDIANA UNIVERSITY GIVES
 *NO WARRANTIES AND MAKES NO REPRESENTATION THAT SOFTWARE IS FREE OF 
 *INFRINGEMENT OF THIRD PARTY PATENT, COPYRIGHT, OR OTHER PROPRIETARY RIGHTS. 
 *INDIANA UNIVERSITY MAKES NO WARRANTIES THAT SOFTWARE IS FREE FROM "BUGS", 
 *"VIRUSES", "TROJAN HORSES", "TRAP DOORS", "WORMS", OR OTHER HARMFUL CODE.  
 *LICENSEE ASSUMES THE ENTIRE RISK AS TO THE PERFORMANCE OF SOFTWARE AND/OR 
 *ASSOCIATED MATERIALS, AND TO THE PERFORMANCE AND VALIDITY OF INFORMATION 
 *GENERATED USING SOFTWARE.
 */
package cgl.narada.matching;


/**
   The EventId Factory is reponsible for the generation of EventId's that
   are unique both in space and time. 

   @author Shrideep Pallickara
   $Revision$
   $Date$
*/

public class EventIdFactory { 

  /** Every issuing client is assigned a unique ID. This reduces the uniqueness
      problem to a point in space */
  private int clientID;
  /** The time in milli-seconds  */
  private long timeStamp;
  /** We use this so that our issue rate isn't determined by the granularity
      of the clock in the underlying system. The sequence numbers start from
      zero and continue till it reaches Short.MAX_VALUE
  */
  private short seqNum;
  /** This is something which needs to be advanced by the client, for every 
      re-join after a disconnected mode operation */
  private short incarnationNumber;
  
  
  /** This is used the first time a client starts issuing events 
      @param _clientID The client ID .
   */
  public EventIdFactory(int _clientID) {
    clientID = _clientID;
    timeStamp = System.currentTimeMillis();
    seqNum    = 0;
    incarnationNumber =0;
  }
  
  /** This is used by a client, after it has been in the disconnected mode
      for sometime and when it joins in it has a different incarnation number.
      This incarnation number is usually incremented every time a client
      joins back in. 
      @param _clientID The ID assigned to the client.
      @param _incarnationNumber The incarnation number for the client in
      question.
  */
  public EventIdFactory(int _clientID, short _incarnationNumber) {
    clientID = _clientID;
    incarnationNumber =  _incarnationNumber;
    timeStamp = System.currentTimeMillis();
    seqNum    = 0;
  }
  
  /** This gets the next EventId that is a logical successor to the eventID
      that was previously created by the factory 
      @return Successor to the eventID that was previously created
  */
  public EventId getNextID() {
    if (seqNum == Short.MAX_VALUE) {
      timeStamp = System.currentTimeMillis();
      seqNum = 0;
    }
    seqNum++;
    return new EventId(clientID, timeStamp, seqNum, incarnationNumber);
  }
  
  public static void main(String[] args) {
    EventIdFactory eventFactory = new EventIdFactory(123);
    for (int i=0; i<10; i++) {
      System.out.println(eventFactory.getNextID());
    }
  }
  
}

